Maybe. But we do know that Mercedes is at the very worst the most powerful engine of the lot, perhaps with the Ferrari close enough on race-day. So when a car, like the McLaren or the RedBull do a great job with a clearly and undisputed less powerful engine to keep up or even win the occasional race on performance, I do think that has a lot to do with chassis and aero efficiency.
Not saying the Mercedes isn't good - it's clearly the best car of all the cars running a Mercedes power unit, but comparing it to other cars running a "compromised" engine, well...
In other words, this season at least, we will get to compare the RedBull, the McLaren and the Renault team from an aero and chassis perspective given they are all running the same power-unit. If McLaren are not on the same level of RedBull, well, we can draw conclusions from that. Maybe they need some time to get the engine integration right or their chassis just isn't as strong as we thought... Either way, I think RedBull will be difficult to beat with the extensive knowledge they have on the Renault powerunit and if McLaren happen to be close to RedBull, well, I'd be impressed (unless RB have some issues or something, like i.e. beginning of last season).